This invention relates to a warning system for traffic routes at an avalanche danger hillside. To detect avalanche falls at their beginning already, i.e. in the zone of initiation, is of great importance for warning, protection and rescuing measures to possibly be initiated. The most important measure is a timely blocking, depending on the falling period of the avalanche in relationship to the traveling speed on the traffic route and a possible releasing of traffic again. For this purpose, predominantly mechanical systems are known which indicate avalanche falls at individual points or along a cross course of a hillside, namely e.g. wires strung across wooden pegs which are torn by a falling avalanche, or yieldable rods movable about an axis with electrical contacts. The former system has the disadvantage that after each incidence new wires must be strung, whereas the latter system is endangered by creeping snow and calls for specific measures in order to avoid a freezing. Large hill or mountain areas cannot be economically supervised with the conventional mechanical systems.
Efforts have generally been made by the inventor to use CW Doppler radar for avalanche supervision, as known for burglary alarm systems. These systems, however, already respond to small motions in the proximity of the antenna, e.g. by a bird; they also are hardly able to distinguish a snow slide from a transverse or uphill movement of an animal. The many erroneous alarms to be expected reduce the observation of an alarm signal in the event of an avalanche risk up to unusability of the entire system. Also, with one Doppler radar device alone a large hill or mountain area can hardly be effectively supervised, since the problems with two differently intense signals become more difficult for CW radar with increasing magnitude.